The outer membrane of Escherichia coli functions as a barrier which allows the passsive diffusion of hydrophilic molecules while protecting the cell from detergents such as deoxycholate. We have found that the predominant outer membrane proteins called porin proteins, have a role in this barrier function for when mutant strains missing demonstrable amounts of porin were isolated, the uptake of sugars, amino acids and nucleotides was markedly reduced. We have found that at least 4 of the predominantly outer membrane proteins are functionally and/or immunologically related.